i was also unable to update to Facebook 1.4. i'm running uncommon sense 1.0. to fix it, i manually renamed the Facebook APK using the following steps: plug phone into computer via USB, reboot into recovery, mount the 'system' partition', open a command prompt, run adb shell, and run 'mv /system/app/Facebook.apk /system/app/Facebook.apk.bak'. this essentially 'removes' the app, without actually deleting the file (just in case you run into a problem, you can rename the file back to Facebook.apk, and the original app is back). i then rebooted the phone, and was able to install the facebook update.